Lyophilized : What are Lyophilized Products?

Now a days, the consumer requires food products with a longer shelf life than the fresh product, and at the same time maintaining all the nutritional properties, odor , color and flavor . By dehydrating a product by lyophilization, these properties can be maintained since the products are frozen and dehydrated under vacuum .

Lyophilization is one of the most widely used methods for the conservation of microorganisms due to its' numerous advantages, among which the prolonged survival time stands out. The selection of additives that allow achieving both a good appearance and prolonged stability of the lyophilized material is one of the most important aspects to consider when using this method.

 

Definition

Lyophilization is a process that consists of drying a previously frozen product, achieving sublimation of the ice under vacuum. It is therefore the direct passage from ice ( solid ) to gas ( steam ), without at any time water appearing in its liquid state . A dry, spongy dough of more or less the same size as the original frozen dough is obtained, improving its stability and being easily redissolved in water.

 

Lyophilization stages

The Lyophilization process basically consists of four stages:

 1. Freeze the product.

 2. Apply the vacuum.

 3. The ice sublimated into water vapor and this is extracted from the drying chamber.

 4. Once this process is finished, the product is removed from the freeze dryer and is ready to be packed and stored

 It is carried out at temperatures below that of total solidification , that is, the product must be frozen at temperatures between 10 and 15 ºC below its eutectic temperature to avoid the formation of H2O clots.

 Initial Freeze

It is a prior and mandatory operation. The duration time depends on several factors such as the quantity, concentration and nature of the product. In general terms, we can say that adequate freezing is the basis for the lyophilized product to present optimum appearance conditions, preservation of its original properties and rapid rehydration.

 Sublimation or primary drying

It is the stage in which most of the free water goes into steam. The parameters temperature, pressure and time can be modified independently but they are closely related, it is not possible to modify one without affecting the others, so their effects must be considered and analyzed together at all times.

Secondary desorption or desiccation

Its mission is to eliminate the last traces of water vapor, evaporating the unfrozen water bound to the product. It is carried out at a temperature lower than the denaturation of the product and a final humidity with values ​​less than 1% is achieved .

 

Advantages of the Lyophilization technique

1-The temperature to which the product is subjected is below that to which many unstable substances undergo chemical changes.

 2-Due to the low temperature that is operated, the loss of volatile constituents is minimal, the danger of microbial contamination is reduced and the enzyme preparations do not suffer alterations.

3-The oxidation phenomena are eliminated, since it is operated and packed under high vacuum.

4-The great porosity of the product quickly facilitates reconstitution by the addition of water or the appropriate solvent.

5-As the remaining humidity is negligible, the product can be stored for an unlimited time, constituting a product of long stability.

Characteristics of the final product

• Optimal stability

• Easy, fast and complete solubility

• Unlimited conservation

• Good protection against harmful external influences

• Quick availability of use.

Benefits

• The product maintains the aroma , flavor and nutrients for as long as possible .

• Instant rehydration.

• Low weight for easy handling and transport.

• No need for refrigeration during transport and storage.

• Long conservation period due to the elimination of 95% -99.5% of the water.

• Little loss of activity of the ingredients.

• Small decrease in volatility of chemicals, nutrients and heat sensitive components .

• With minimal changes) n the + s properties, since the effect of the growth of microorganisms and enzymes cannot be exerted at low temperatures

Disadvantages of Freeze Drying

1- It is an expensive process.

2- Need for qualified personnel in the operation and maintenance of the equipment.

3- High investment cost of facilities and equipment.

 Applications

Lyophilization is a process that is applied to three broad categories of biological products:

 • Blood plasma , serum, hormone solutions , pharmaceuticals, and food ;

 • Surgical transplants such as arteries , skin and bones .

• In living cells destined to remain in that state for long periods of time. They include bacteria , viruses, and yeast (but not mammalian cells ).

Examples of use

• Coffee , tea and other extracts.

• Vegetables and fruits

• Meats and seafood

• Prepared meals

• Dairy products

• Dyes, pharmaceuticals, pigments .

Importance in the Food Industry

Lyophilization is of utmost importance for the preservation of food products because:

• Stops the growth of microorganisms ( fungi , mold and others).

• Inhibits deterioration due to chemical reaction (color and flavor change, rancidity, loss of nutritional properties).

• Facilitates distribution and storage (the weight of the product decreases by up to 90% and it is not necessary to maintain a cold chain).

• In addition, it has two other notable virtues: the treated product does not change shape and is easily re-hydratable.

 That significant cost has relegated it to the production of medicines or foods of high specific value, such as prawns, instant soluble coffee, rations for mountaineers and other high-demand sports, military rations and for astronauts . In recent years, the use of freeze-dried foods (pieces of meat and vegetables) combined with other heat-dehydrated foods has increased, to produce more affordable instant soups and sauces .

 

Technological process

In conventional industrial facilities the vacuum (0.1 to 4.0 mmHg) is achieved by combining vacuum pumps and large "cold traps" that must work at -40 or -50 ºC, to freeze the water that is extracted from the product and avoid that happens to the bomb. This technology is relatively expensive, both in the investment corresponding to the capital asset, and in its operation and maintenance costs, due to the large number of precision moving parts involved in the production of the vacuum that must work at very low temperatures.